1. Field of Invention
The present invention relates to a wireless broadband technology, and more particularly to a call admission control method.
2. Description of Related Arts
WiMAX (World Interoperability for Microwave Access) is a wireless metropolitan area network technology, and a new proposed air interface standard for the microwave and millimeter-wave frequency band. Compared with the other technologies, WiMAX can be applied to the barrier-free, long-distance (several kilometers) and large-capacity (10M) wireless data transmission, the large-capacity data acquisition and the long-distance wireless broadband transmission for field operations, the real-time audio and video capture for the emergency system deployment of earthquakes, forest fire prevention, floods and emergencies, and the “last mile” wireless broadband access for wireless broadband remote transmission equipments, homes and businesses. Therefore, WiMAX has a huge market demand.
In WiMAX wireless broadband networks, call admission control (CAC) is the key to ensure the quality of service (QoS), and plays an important role in reducing network congestion and improving utilization ratio of network resources.
Nowadays, many call admission control methods have been proposed, in which a more typical control method is the guard channel strategy.
In the guard channel strategy, the base station system has always reserved a maximum bandwidth for every business flow till the service period of the business flow ends. Also, the bandwidth threshold of the base station system is set, when the total reserved bandwidth of the base station system exceeds the bandwidth threshold, the base station system will refuse to admit the low priority business and only admit the high priority business. Accordingly, the characteristics of the guard channel strategy are improving the rejection rate of the low priority business and reducing the utilization rate of the base station system resources so as to reduce the rejection rate of the high priority business, thus ensuring the quality of service of the high priority business. The biggest drawback of the existing guard channel strategy is explained as follows. The bandwidth reserved by the base station system for the admitted business flow can not be fully used in the traffic real-time changes. If admitting a new business flow damages the quality of service of the admitted business flow, in spite that whether the normal communication of the admitted business flow is affected or not, the new business flow will be not admitted. Simultaneously, the guard channel strategy limits the admission rate of the low priority business at a very low level, so it lacks fairness for various user demands with different priorities.